The present invention relates to a color signal adjustment device that adjusts first through third color signals according to lookup tables and to an image display apparatus using the same.
An image display apparatus like a projector has a color signal adjustment device for correcting non-linear input-output characteristics (gamma characteristics) of a display device, such as a liquid crystal panel. The color signal adjustment device utilizes lookup tables for correction of the input-output characteristics. Each lookup table represents a mapping of linear tone values of each color signal, red (R), green (G), or blue (B) to non-linear tone values for correction of the gamma characteristics.
FIG. 10 is a block diagram schematically illustrating the structure of a prior art color signal adjustment device. The prior art color signal adjustment device 300 includes three address selector circuits 310R, 310G, and 310B corresponding to respective color signals R, G, and B and three RAMs 320R, 320G, and 320B, as well as one data selector 330. Lookup tables corresponding to the color signals R, G, and B are respectively stored in the three RAMs 320R, 320G, and 320B.
The first address selector 310R selects either an R color signal RI or an address signal AD supplied via an external address bus (not shown) as an input address signal in response to a first address selection signal SLTR and supplies the selected input address signal to the RAM 320R. In a similar manner, the second address selector 310G selects either a G color signal GI or the address signal AD as an input address signal in response to a second address selection signal SLTG and supplies the selected input address signal to the RAM 320G. The third address selector 310B selects either a B color signal BI or the address signal AD as an input address signal in response to a third address selection signal SLTB and supplies the selected input address signal to the RAM 320B.
The data selector 330 selects one of output color signals RO, GO, and BO read from the three RAMs 320R, 320G, and 320B in response to the first through the third address selection signals SLTR, SLTG, and SLTB, and supplies the selected output color signal as reading data RD to an external data bus. Writing data WD is supplied to the three RAMS 320R, 320G, and 320B via an external data bus.
Read-write signals WRR, WRG, and WRB are supplied to control the reading and the writing operations from and into the respective RAMs 320R, 320G, and 320B. In the reading process of the respective RAMs 320R, 320G, and 320B, data corresponding to the input address signals are read and output as the respective output color signals RO, GO, and BO.
During the operation of the image display apparatus, the respective color signals RI, GI, and BI are selected in the first through the third address selectors 310R, 310G, and 310B as the input address signals into the RAMS 320R, 320G, and 320B. Corresponding data are read from the lookup tables stored in the RAMs 320R, 320G, and 320B and are output as the output color signals RO, GO, and BO.
The lookup tables for the respective colors are stored into the RAMs 320R, 320G, and 320B of the corresponding colors according to an exemplified procedure discussed below.
The procedure first stores the lookup table for the color R into the RAM 320R of the color R. The procedure selects the address signal AD supplied via the address bus in the first address selector 310R as the input address signal into the RAM 320R. The procedure then writes the writing data WD supplied via the data bus at the address in the RAM 320R specified by the address signal AD. At this moment, the output of the RAM 320R is generally cut off, and the output color signal RO is fixed to either a high level or a low level by a connected terminal resistance (not shown). Alternatively a variation in data at the address may be output directly.
In the same manner as that for the RAM 320R of the color R, the procedure stores the lookup table for the color G into the RAM 320G of the color G by selecting the address signal AD in the second address selector 310G as the input address signal into the RAM 320G of the color G. Like the RAMs 320R and 320G of the colors R and G, the lookup table for the color B is stored into the RAM 320B of the color B by selecting the address signal AD in the third address selector 310B as the input address signal into the RAM 320B of the color B.
As described above, the lookup tables for the respective colors are sequentially stored into the three RAMs 320R, 320G, and 320B of the corresponding colors.
Storage of the lookup tables for the respective colors into the RAMs 320R, 320G, and 320B of the corresponding colors is generally carried out in the course of initializing the image display apparatus.
In some cases, however, it is required to rewrite and update the lookup tables for the respective colors stored in the RAMs 320R, 320G, and 320B of the corresponding colors during the operation of the image display apparatus. For example, there may be a requirement of rewriting the lookup tables to adjust the contrast, the brightness, and the color tone.
During the operation of the image display apparatus, lookup tables are generally written in a blanking period. The lookup tables stored in the RAMs 320R, 320G, and 320B are sequentially rewritten as mentioned above. It accordingly takes a relatively long time to complete the rewriting operation. The rewriting may thus be performed during the display. The rewriting during the display causes output of specific data intrinsic to the rewriting operation, for example, high-level data or low-level data in the above example. This disadvantageously causes superimposition of noise on the displayed image.
One applicable procedure to prevent superimposition of noise does not use the lookup table for display only in the course of rewriting the lookup table. In this case, however, the displayed image during the rewriting of the lookup table is defined by color signals without gamma correction and adjustment of the contrast or brightness. This disadvantageously changes the color tone of the displayed image.
The object of the present invention is thus to solve the drawbacks of the prior art technique discussed above and to provide a technique that enables lookup tables to be rewritten without causing superimposition of noise in a displayed image or a variation in color tone of the displayed image during operation of an image display apparatus.
At least part of the above and the other related objects is attained by an image display apparatus of the present invention, which includes: a color signal adjustment module that adjusts first through third color signals corresponding to first through third colors expressing a color image; an image display module that displays a color image defined by first through third output color signals from the color signal adjustment module; and an adjustment control module that controls the color signal adjustment module. The color signal adjustment module has: first through fourth RAMs available as lookup tables for adjusting color signal levels; an address selection module that replaceably allocates the first through the third color signals and a predetermined address signal to input address signals of the first through the fourth RAMs, in response to a preset selection signal from the adjustment control module; and a data selection module that selectively outputs at least three output signals among output signals from the first through the fourth RAMs as the first through the third output color signals corresponding to the first through the third colors, in response to the preset selection signal.
During the normal operation, the first through the third lookup tables corresponding to the first through the third color signals are allocated to three RAMs selected among the first through the fourth RAMs, and one RAM is set in the vacant state (namely the RAM is not used for storage of the lookup table). The first through the third lookup tables may be updated according to the following procedure. In one example, it is assumed that the first through the third original lookup tables are stored in the first through the third RAMs and that the fourth RAM is set in the vacant state. The procedure sets the first updated lookup table into the fourth RAM. This causes the first RAM, in which the first original lookup table has been stored, to be set in the vacant state. The procedure then sets the second updated lookup table into the first RAM in the vacant state. This causes the second RAM, in which the second original lookup table has been stored, to be set in the vacant state. The procedure subsequently sets the third updated lookup table into the second RAM in the vacant state.
In this manner, one of the four RAMs is sequentially set in the vacant state. The arrangement of sequentially setting the updated lookup tables into the RAMs in the vacant state ensures the new settings of the lookup tables by utilizing only the RAMs that are not currently involved in adjustment of color signals. This arrangement desirably enables the lookup tables to be rewritten without causing superimposition of noise in a displayed image or a variation in color tone of the displayed image, which is observed in the prior art apparatus during the operation of the image display apparatus.
The present invention is also directed to a color signal adjustment device that adjusts first through third color signals corresponding to first through third colors expressing a color image. The color signal adjustment device includes: first through fourth RAMs available as lookup tables for adjusting color signal levels; an address selection module that replaceably allocates the first through the third color signals and a predetermined address signal to input address signals of the first through the fourth RAMs, in response to a preset selection signal; and a data selection module that selectively outputs at least three output signals among output signals from the first through the fourth RAMs as first through third output color signals corresponding to the first through the third colors and a predetermined output signal, in response to the preset selection signal.
Application of the color signal adjustment device of the present invention to the color signal adjustment module gives the image display apparatus of the present invention.